FIG. 6 shows a conventional AC plasma display panel and its driving circuit. The AC plasma display panel 1, herein after referred to as "panel" for clarity, has 2M rows of scan electrodes SCN(1)-SCN(2M) and sustain electrodes SUS(1)-SUS(2M), and N columns of data electrodes D(1)-D(N) each extending perpendicular to scan and sustain electrodes, forming a 2M by N matrix. Each of scan electrodes SCN(i) pairs with a corresponding sustain electrode SUS(i) so that the paired scan and sustain electrodes cooperate with one of the crossing data electrodes D(j) (integer j:1-N) to form a cell where an electric discharge will occur.
In this panel 1, lead wires of the paired scan and sustain electrodes, SCN(i) and SUS(i), are extended out in opposite directions. Also, the lead wires of the neighboring scan electrodes, for example, SCN(1) and SCN(2), are extended out in opposite directions. Likewise, the lead wires of the neighboring sustain electrodes, for example, SUS(1) and SUS(2), are extended out in opposite directions. That is, in this arrangement, the odd number of scan electrodes SCN(1), SCN(3), . . . . , SCN(2M-1) are led out to the left side of the panel and then electrically connected with a scan electrode drive circuit 2a for driving scan electrodes with odd number. On the other hand, the even number of scan electrodes SCN(2), SCN(4), . . . , SCN(2M) are led out to the right side of the panel and then electrically connected with a scan electrode drive circuit 2b for driving scan electrodes with even number. Further, the even number of sustain electrodes SUS(2), SUS(4), . . . , SUS(2M) are led out to the left side of the panel and then electrically connected with a sustain electrode drive circuit 3b for driving sustain electrodes with even number. On the other hand, the odd number of sustain electrodes SUS(1), SUS(3), . . . , SUS(2M-1) are led out to the right side of the panel and then electrically connected with a sustain electrode drive circuit 3a for driving sustain electrodes with odd number. In addition, lead wires of the data electrodes D(1)-D(N) are extended out upwardly and then electrically connected with a data electrode drive circuit 4 for driving the data electrodes.
Referring again FIG. 6 as well as FIG. 7 showing a time chart, operations of the conventional panel will be described briefly. Firstly, in a period for writing, sustain drive circuit 3a or 3b applies no signal or voltage to sustain electrodes SUS(1)-SUS(2M). For scanning in the first row scan electrode SCN(1), among data electrodes D(1)-D(N), selected one or more data electrodes D(j) corresponding to discharge cells for displaying are applied with a certain positive write pulse of +Vw volts from the data electrode drive circuit 4, and the first scan electrode SCN(1) is applied with a certain negative scan pulse of -Vs volts from scan electrode drive circuit 2a. This causes an electric discharge (writing discharge) at each of the intersections of the selected data electrodes D(j) and scan electrode SCN(1).
Then, for scanning in the second row scan electrode SCN(2), selected one or more data electrodes D(j) corresponding to discharge cells for displaying are applied with the write pulse of +Vw volts from the data electrode drive circuit 4, and the second scan electrode SCN(2) is applied with scan pulse of -Vs volts from another scan electrode drive circuit 2b. This causes the electric discharge (writing discharge) at each of the intersections of the selected data electrodes D(j) and scan electrode SCN(2). Similar operations are performed successively for scan electrodes SCN(3) to SCN(2M), causing electric discharges at discharge cells at intersections of data electrodes D(j) and scan electrodes SCN(3) to SCN(2M).
Secondly, in a subsequent period for sustaining, sustain electrode drive circuits 3a and 3b apply a negative sustain pulse of -Vm volts to every sustain electrodes SUS(1)-SUS(2M). This causes an initial sustain discharge between scan and sustain electrodes, SCN(i) and (i), in each of the discharge cells where the writing discharge has occurred in the write period. At this moment, a sustain discharge current flows from scan electrode drive circuit 2a through odd scan electrodes SCN(2K-1) (integer K: 1 to M) and then odd sustain electrodes SUS(2K-1) toward sustain electrode drive circuit 3a. Also, a sustain-discharge current flows from scan electrode drive circuit 2b through even scan electrodes SCN(2K) and then even sustain electrodes SUS(2K) toward sustain electrode drive circuit 3b.
Afterwards, sustain electrode drive circuits 3a and 3b apply no voltage to every sustain electrodes SUS(1)-SUS(2M), but scan electrode drive circuits 2a and 2b apply negative sustain pulse of -Vm volts. This causes a sustain discharge between scan and sustain electrodes, SCN(i) and SCN(i), in each of the discharge cells where the writing discharge has occurred. At this moment, sustain discharge current flows from sustain electrode drive circuit 3a through the odd sustain electrodes SUS(2K-1) and then odd scan electrodes SCN(2K-1) toward scan electrode drive circuit 2a. Also, sustain discharge current flows from sustain electrode drive circuit 3b through even sustain electrodes SUS(2K) and then scan electrodes SCN(2K) toward scan electrode drive circuit 2b.
Subsequently, scan electrodes SCN(1)-SCN(2M) and sustain electrodes SUS(1)-SUS(2M) are applied with the negative sustain pulse of -Vm volts alternatively from scan electrode drive circuits 2a and 2b and sustain electrode drive circuits 3a and 3b. This retains sustain discharge between scan and sustain electrodes, SCN(i) and (i), at each of the discharge cells where the writing discharge have occurred. This in turn allows sustain discharge current to flow from sustain electrode drive circuit 3a to scan electrode drive circuit 2a and from sustain electrode drive circuit 3b to scan electrode drive circuit 2b. In addition, sustain discharge current flows from scan electrode drive circuit 2a to sustain electrode drive circuit 3a and from scan electrode drive circuit 2b to sustain electrode drive circuit 3b.
In the subsequent period for erasing, all sustain electrodes SUS(1)-SUS(2M) are applied with a short negative erase pulse of -Ve volts from sustain electrode drive circuits 3a and 3b, causing an erase discharge at each of the discharge cells to erase sustain discharge.
With the operations described above, one frame of image is displayed on the panel by the use of light emitted during sustain discharge.
Referring to FIG. 8, there is illustrated a schematic enlarged plan view of a part of the panel shown in FIG. 6, in particular electrodes positioned in rows from (2K-1) to (2K). In this drawing, sustain discharge current flowing at the first sustain discharge in sustain period is shown. In particular in this drawing, bold arrows indicate the directions along which sustain discharge current flows in respective electrodes, and normal arrows indicate the directions along which sustain discharge current flows from one electrode to another. As can be seen from the drawing, the direction that sustain electrode current flows in the odd scan and sustain electrodes, SCN(2K-1) and (2K-1), is opposite to that sustain discharge current in the even scan and sustain electrodes, SCN(2K) and SUS(2K). With this opposite flows of sustain discharge current in the odd and even electrodes, a vector of electromagnetic wave caused from the odd scan and sustain electrodes, SCN(2K-1) and SUS(2K-1) opposes to and counteracts another vector of that caused from the even scan and sustain electrodes, SCN(2K) and SUS(2K). This means that, because most of the electromagnetic waves or noises are those generated by sustain discharge current running through the electrodes at sustain discharge, a panel with a reduced electromagnetic noise can be provided.
The conventional panel, however, is designed so that scan electrode drive circuits 2a and 2b and also sustain electrode drive circuits 3a and 3b are provided on opposite sides for odd and even electrodes. Therefore, it has been found that even a slight time shift between operations of scan electrode drive circuits 2a and 2b or between sustain electrode drive circuits 3a and 3b renders the counteraction of the electromagnetic noises unstable.
Descriptions will be made to the reasons of the unstable counteraction with reference to FIGS. 9(a) to 9(e) showing waveforms of sustain pulse voltage of -Vm volts and waveforms of sustain discharge current that flows through scan and sustain electrodes, at the first sustain discharge in sustain period. It should be noted that in each of FIGS. 9(a) to 9(e) a horizontal axis, i.e., time axis, has different scales at its left and right portions.
Specifically, FIG. 9(a) illustrates the waveform of voltage applied to the odd scan electrodes SCN(2K-1) relative to sustain electrode drive circuit 3a when sustain pulse voltage of -Vm volts is applied from sustain electrode drive circuit 3a to the odd sustain electrode (2K-1).
Also, FIG. 9(b) illustrates the waveform of sustain discharge current flowing from scan electrode drive circuit 2a through the odd scan electrodes SCN(2K-1) and also odd sustain electrode SUS(2K-1) to sustain electrode drive circuit 3a when sustain pulse of -Vm volts is applied from sustain electrode drive circuit 3a to the odd sustain electrode (2K-1). FIG. 9(c) illustrates the waveform of voltage applied to the even sustain electrodes SUS(2K) relative to scan electrode drive circuit 2b when sustain pulse of -Vm volts is applied from sustain electrode drive circuit 3b to the even sustain electrodes SUS(2K).
Further, FIG. 9(d) illustrates the waveform of sustain discharge current flowing from sustain electrode drive circuit 3b through the even sustain electrode SUS(2K) and also even scan electrode SCN(2K) to scan electrode drive circuit 2b when sustain pulse of -Vm volts is applied from sustain electrode drive circuit 3b to the even sustain electrode SUS(2K).
Furthermore, FIG. 9(e) illustrates a resultant current waveform of current waveforms shown in FIGS. 9(b) and 9(d).
It should be noted that the voltage and current waveforms are illustrated with the flowing directions of the current in order to effectively describe the counteraction of the electromagnetic noises.
As shown in FIGS. 9(b) and 9(d ), the discharge sustain current is a resultant of two currents, Id and Ic. The current Id, which serves to the actual light emission, starts flowing slightly after the application of sustain pulse voltage. The current IC, which flows in response to a capacitance between scan and sustain electrodes, has an extremely narrow period, or is in the form of sharp peak. Therefore, the current IC is ineffective for the light emission, but causes unwanted electromagnetic noises.
Also, as indicated by solid lines in FIGS. 9(b) and 9(d), if sustain electrode drive circuit 3a drives in synchronous with sustain electrode drive circuit 3b and thereby sustain pulses from those circuits are applied simultaneously, the resultant current waveform is minimized as best shown in FIG. 9(e). This means that the electromagnetic noises counteract to each other. On the other hand, as shown by dotted lines in FIGS. 9(c) and 9(d), if sustain electrode drive circuit 3a drives out of synchronous with sustain electrode drive circuit 3b and thereby sustain pulses from those circuits are applied in different times, the resultant current waveform has two sharp peaks of opposite polarities as shown in FIG. 9(e). This means that the electromagnetic noises does not counteract to each other, resulting in increased electromagnetic noises.
Further, as shown in FIG. 9(b) or 9(d), typically, the ineffective current waveform IC is a sharp, narrow peak with a period of several nanoseconds. Then, in order to minimize the resultant current waveform as shown by solid lines in FIG. 9(e), a time shift between operations of sustain electrode drive circuits 3a and 3b should be minimized. For those purposes, responses of the circuits as well as response stability thereof should be reduced to about several hundred picoseconds, which is considered to be impossible. In view of above, the counteraction of the electromagnetic noises is not ensured positively, which is a great problem to be solved.
Referring to FIG. 22, an AC plasma display system includes a display panel and its driving units in which an image is displayed by sustaining discharge between neighboring scan and sustain electrodes. As can be seen from the drawing, the panel 1a includes M rows of scan electrodes SCN(1)-SCN(M), and M rows of sustain electrodes SUS(1)-SUS(M) each extending parallel to scan electrodes, and N columns of data electrodes D(1)-D(N). Each row consists of paired scan and sustain electrodes, and scan and sustain electrodes are positioned alternately. Scan and sustain electrodes are led out in the opposite directions and then connected with scan electrode drive circuit 2 and sustain electrode drive circuit 3, respectively. Two scan electrodes defining SCN(1) are led out on the left side of the panel where they are electrically connected with scan electrode drive circuit 2, and two sustain electrodes defining SUS(1) are led out on the right side of the panel where they are electrically connected with sustain electrode drive circuit 3.
Intersections between paired scan and sustain electrodes and data electrodes define discharge cells, indicated at C(11)-C(MN). Therefore, in this panel, discharge cells each include two scan and sustain electrodes, forming M by N matrix.
Referring to FIG. 23 showing an operational time chart, operations of the panel will be described. Firstly, in the write period all of sustain electrodes SUS(1)-SUS(M) is retained at zero volt by sustain electrode drive circuit 3. In the first row or line scanning, among data electrodes D(1)-D(N), one or more data electrodes D(j) (integer j: 1-N)for displaying image are applied with positive write pulse of +Vw volts from the data electrode drive circuit 4, and the first row scan electrode SCN(1) is applied with negative scan pulse of -Vs volts. This causes a write discharge at the discharge cell C(1,j), intersection of the data electrode D(j) and scan electrode SCN(1).
Secondly, in the second row or line scanning, among data electrodes D(1)-D(N) one or more data electrodes D(j) for displaying image are applied with positive write pulse of +Vw volts from the data electrode drive circuit 4, and the second row scan electrode SCN(2) is applied with negative scan pulse of -Vs volts. This causes the write discharge at the discharge cell C(2,j), intersection of the data electrode D(j) and scan electrode SCN(2).
Similar operations are repeated for the remaining rows, i.e., up to M row, causing writing discharge at selected discharge cells.
In the next sustain period, all of sustain electrodes SUS(1)-SUS(M) are applied from sustain electrode drive circuit 3 with the negative sustain pulse of -Vm volts. This causes the initial sustain discharge between scan electrode SCN(i) (integer i:1-M) and sustain electrode SUS(i) at the discharge cell C(i,j) where the write discharge has been occurred. This in turn causes a certain current to flow from scan electrode drive circuit 2 through scan electrode SCN(i) and then sustain electrode SUS(i) toward sustain electrode drive circuit 3. Next, scan electrodes SCN(1)-SCN(M) and sustain electrodes SUS(1)-SUS(M) are applied with negative sustain pulse of -Vm volts alternately from scan electrode drive circuit 2 and sustain electrode drive circuit 3. This retains sustain discharge between scan electrode SCN(i) and sustain electrode SUS(i) at each of the discharge cells C(i,j) where the write discharge has occurred. This in turn causes a certain current to flow from sustain electrode drive circuit 3 through sustain electrode SUS(i) and then scan electrode SCN(i) toward scan electrode drive circuit 2 and from scan electrode drive circuit 2 through scan electrode SCN(i) and then sustain electrode SUS(i) toward sustain electrode drive circuit 3, alternately. Sustain discharge emits light for display.
In the next erase period, all of sustain electrodes SUS(1)-SUS(M) are applied with negative narrow pulse of -Ve volts from sustain electrode drive circuit 3, causing an erasing discharge to erase sustain discharge.
With the above-described operations, one frame of image is displayed on the panel. Also, in each of discharge cell two discharges are generated, each discharge is generated between paired scan and sustain electrodes. This causes that an extended light emission is provided at each discharge cell, increasing the brightness of the resultant image.
However, the conventional AC plasma display panel has a drawback that intense electromagnetic noises are generated by sustain discharge current at sustain discharging.
Descriptions will be made to the drawback in detail hereinafter. Referring to FIG. 24, there is shown a part of the panel in which electrodes of from (i-1)th to (i+1)th rows are electrically connected with scan electrode drive circuit 2 and sustain electrode drive circuit 3. Also, FIG. 24 shows sustain discharge current (shown by solid lines) generated by an application of negative sustain pulse of -Vm volts to sustain electrodes SUS(1)-SUS(M) at a certain time (t) in sustain period shown in FIG. 23. As can be seen from the drawing, in each row two sustain discharge currents flowing in the paired scan and sustain electrodes run in the same direction. For example, in row (i) the first discharge current from one scan electrode SCN(i,a) to one sustain electrode SUS(i,a) flows in the same direction as the second discharge current from the other scan electrode SCN(i,b) to the other sustain electrode SUS(i,b). This means that in each row the two sustain discharge currents flows in the same direction from scan to sustain electrodes, causing electromagnetic noises with the same phase due to sustain discharge currents. Also, the electromagnetic noises with the same phase are superimposed to generate a greater electromagnetic noise which would be emitted from the panel. Also, as indicated by dotted lines in FIG. 24, in each row the current flows through the capacitance between both paired scan and sustain electrodes, e.g., from scan electrode SCN(i,b) to sustain electrode SUS(i,a) in the same direction, i.e., left to right. Also, as indicated by broken lines in FIG. 24, the current flows through the capacitance between both paired scan and sustain electrodes, e.g., from scan electrode SCN(i,a) to sustain electrode SUS(i-1,b) in the same direction, i.e., left to right. Therefore, the electromagnetic noise generated by the current flowing through capacitance has the same phase as that generated by sustain discharge current in every row.
In view of above, the flowing direction of sustain discharge current from scan to sustain electrodes as well as the flowing direction of the current from scan electrode through the capacitance to sustain electrode in one row is the same as those in another row, causing an intense electromagnetic noise, which is a great problem to be solved.